1. Field of the Invention
The present invention relates to block copolymer and a substrate processing method, and more particularly to a photosensitive block copolymer and a substrate processing method by which a micropattern is formed by radiation exposure that uses the photosensitive block copolymer.
2. Description of the Related Art
In the field of electronic devices that require nanoorder microprocessing, starting with semiconductor devices, a demand has been growing for increased density and degree of integration of the devices.
A photolithographic process plays the most important role in forming microcircuit patterns in fabrication of semiconductor devices. Most photolithographic processes are presently implemented by reduction projection exposure, but the resolution of such process is limited by a light diffraction limit and is about one third of the light source wavelength. For this reason, the wavelength is decreased by using an excimer laser for an exposure light source, thereby making it possible to conduct microprocessing of an order of 100 nm.
The photolithography advances miniaturization, but also raises a large number of issues that have to be resolved as the light source wavelength is reduced, for example, the increase in the device size, the necessity to develop lenses for the wavelength range, the device cost, and the corresponding resist cost. Furthermore, the aforementioned optical devices require processing that is at least as inexpensive as that of the semiconductor devices.
A method for obtaining a self-structured configuration of microparticles and a method using a microphase-separated structure formed by a block copolymer are known as inexpensive and simple micropatterning methods serving as alternatives for the photolithographic technology (Appl. Phys. Lett., 2586, 68 (1996)).
The method using a microphase-separated structure makes it possible to form a uniform nanostructure over the entire surface of a substrate.
Japanese Patent Laid-Open No. 2002-287377 disclosed the following two methods aimed at the formation of a nanostructure only in the desired position on a substrate.
With the first method, a predetermined area of a block copolymer film is irradiated with a high-energy beam such as an electron beam, thereby cutting (or crosslinking) a polymer chain, and then annealing is performed at a temperature equal to or higher than the glass transition temperature of the block copolymer. With this method a microphase-separated structure is not formed in the irradiated area (or non-irradiated area).
With the second method, an acid is generated by irradiating a predetermined area of a block copolymer film having a radiation-sensitive acid-generating agent added thereto with radiation and then annealing at a temperature equal to or higher than the glass transition temperature of the block copolymer. During annealing, a dissociation reaction (or a polymer chain crosslinking reaction) of a hydrophobic protective group using the generated acid as a catalyst is induced in the irradiated area. As a result, a microphase-separated structure is formed only in the irradiated area (or only in the non-irradiated area).
In the microphase-separated structure formed by these two methods, at least one block is selectively removed by dry etching, wet etching, or ozone ashing, and the underlying substrate is processed by using the remaining blocks and the area where the microphase-separated structure has not been formed as a mask, thereby making it possible to produce a substrate in which a nanostructure is formed only in the desired positions.
However, the first method disclosed in Japanese Patent Laid-Open No. 2002-287377 requires an expensive high-energy beam irradiation device such as electron beam lithography device. The problem associated with the second method is that an acid generated under irradiation serves as a catalyst and side reactions such as modification of the block copolymer or corrosion of the substrate occur during the annealing.